PCI bus do 2 Enumeration when 2 root bridges under 1 host bridge

[Eric Song <EricSong@zhaoxin.com>]

Hi, experts
         If there is 2 root bridges under 1 host bridge on the PCI hierarchy, whether EDK2 Pci bus driver can support it ? the answer is YES, but some confused things in it.

1)       On BDS phase, ConnectController is called for every root bridge, so Pci bus start() will be called for every root bridge.

  VisitAllInstancesOfProtocol (&gEfiPciRootBridgeIoProtocolGuid, ConnectRootBridge, NULL);

2)       In PCI bus driver, Pci start() will do enumeration on the entire host bridge

PciEnumerator()->PciHostBridgeEnumerator->”PciResAlloc->GetNextRootBridge()”

That means Do enumeration on entire host bridge for every one root bridge. So there are 2 enumerations on entire host bridge for my PCI hierarchy.
         What I confused is why do 2 enumerations on entire host bridge by every one root bridge. Since BDS connect controller by one root bridge , Pci bus driver should enumerate corresponding root bridge, But it do the entire host bridge which is the parent of the root bridge.
Or BDS should connect controller by one host bridge, then it will match the pci bus driver ‘s enumeration policy.
In a word, I think it is illogical for current EDKII code.

         Well, the current code execution will do 2 enumerations on host bridge for 2 root bridges under 1 host bridge. Even though 2rd enumeration would be not full enumeration, but do PciEnumeratorLight(), I think it is still not necessary. Whether there is any side effect ?  In another word, current PCI bus driver enumeration can’t be Suitable for 2 root bridges under 1 host bridge or not? It indeed match the PCI hierarchy of 2 host bridges and 1 root bridge under 1 host bridge.

Thanks
Eric



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